What is Ettringite?
Ettringite is a highly hydrated calcium aluminium sulfate that forms fine hexagonal needles in cement, volcanic and hydrothermal environments.
Mineralogy and structure
Reference formula: Ca6Al2(SO4)3(OH)12·26H2O. Ettringite has a channelled structure with a large amount of structural water. Natural and synthetic material may differ in hydration or substitution, so the COD model is labelled as representative where appropriate.
Colour and appearance
Typical colours include colourless, white, pale yellow. The usual acicular, fibrous, radiating habit and vitreous, pearly lustre are useful descriptive features, but colour alone is not diagnostic.
Formation and localities
Ettringite forms in or is associated with alkaline sulfate-rich systems, altered limestones, fumaroles and cement hydration products. Important documented localities include Germany, South Africa, Japan, Italy, the United States and cement-related occurrences worldwide.
Collecting and care
Very fragile and water-rich; protect from drying, heat, impact and uncontrolled humidity changes.
Ettringite in popular symbolism
Modern crystal guides sometimes associate Ettringite with symbolic themes based on colour or collecting tradition. These associations are cultural interpretations, not mineralogical or medical properties.
